1. Field of the Invention
The present invention relates generally to an audio reproducing apparatus for use with a so-called 8-mm video tape recorder (8-mm VTR) or the like.
2. Description of the Prior Art
FIG. 1 of the accompanying drawings shows an arrangement of an audio reproducing apparatus applied to 8-mm video tape recorders according to the prior art.
As shown in FIG. 1, on the recording side, stereophonic left and right signals L and R are respectively amplified by amplifiers 1.sub.L and 1.sub.R and then output to an adder 2 and a subtractor 3, in which they are processed to provide a sum signal (L+R)/2 and a difference signal (L-R)/2, respectively. The sum signal (L+R)/2 is reduced in noise by a noise reduction circuit 4.sub.L and then applied to a frequency modulator circuit 5.sub.L. The frequency modulator circuit 5.sub.L has a carrier of 1.5 MHz, for example. This frequency modulator circuit 5.sub.L frequency-modulates this carrier by the sum signal (L+R)/2 and outputs the frequency-modulated signal to an adder 6. This is also true for the difference signal (L-R)/2. That is, the difference signal (L-R)/2 is reduced in noise by a noise reduction circuit 4.sub.R and output to a frequency modulator circuit 5.sub.R, in which a carrier of 1.7 MHz, for example is frequency-modulated by the difference signal (L-R)/ 2 and then output to the adder 6. The sum and difference signals thus modulated are added by the adder 6 and then recorded on a magnetic tape T by a recording head H.sub.R together with a video signal.
On the other hand, in the reproducing side, a sum signal and a difference signal reproduced from the magnetic tape T by a reproducing head H.sub.p together with the video signal are respectively extracted as carriers of 1.5 MHz and 1.7 MHz by bandpass filters 7.sub.L, 7.sub.R having frequencies of 1.5 MHz and 1.7 MHz, respectively. The frequency component of 1.5 MHz that has been extracted by the bandpass filter 7.sub.L is demodulated by a demodulator circuit 8.sub.L to provide the original sum signal. This sum signal is output through a noise reduction circuit 9L. Similarly, a frequency component of 1.7 MHz that has been extracted by the bandpass filter 7.sub.R is demodulated by a demodulator circuit 8.sub.R to provide the original difference signal which is output through a noise reduction circuit 9.sub.R. The left and right sum and difference signals are supplied to an adder 10 and a subtractor 11 from which they are output from left and right output terminals T.sub.L and T.sub.R as stereophonic reproduced signals L and R, respectively.
Generally, in the stereophonic system, the stereophonic left and right signals L and R contain a center sound such as man's voice (hereinafter referred to as a vocal sound) or the like. This center sound is, when reproduced, localized at the center. Accordingly, if a difference between the left signal L and the right signal R is formed and reproduced, the center sound such as the vocal sound or the like is erased or the output level of the center sound is reduced considerably. In particular, when the user wants to erase the vocal sound in the songs highlighting the vocal sound or the like, it is effective to utilize this difference signal.
As conventional apparatus that can erase the vocal sound based on the difference signal, there are known a CD (compact disc) player, a multi-disc player and so on. These apparatus include a voice erasing circuit for erasing a vocal sound, wherein the difference signal (L-R) is formed from the left and right signals L, R and the vocal sound is erased only to reproduce a musical accompaniment. Thus, the user (listener) can listen to only the musical accompaniment or the user can sing a song to musical accompaniment or background music sound.
According to the above conventional apparatus, however, when the voice erasing circuit is constructed, a differential amplifier composed of an operational amplifier or the like is used in order to form a predetermined difference signal (L-R). For this reason, the number of circuit assemble parts is increased and a space that these circuit assemble parts needs is increased, which unavoidably makes it impossible to make the audio reproducing apparatus compact in size and inexpensive.
Moreover, although the conventional 8-mm video tape recorder includes a stereophonic circuit in which the difference signal (L-R)/2 is formed, if the difference signal (L-R)/2 is reproduced as it is, then a reproduced sound becomes unnatural. As a consequence, such unnatural sound cannot be used as a listener sound or background sound.